1. Field of the Invention
The present invention relates to method and device for measuring the brightness of an object and, in particular, to such method and device for measuring the brightness of an object in photographing the object in flash synchronization using an AE sensor for averaged overall light reading.
2. Description of the Related Art
To measure the brightness of an object, there are available two methods, that is, a spot light reading method and an averaged overall light reading method. The spot light reading method is a method in which the brightness of a main object and the brightness of the background are measured individually and an amount of exposure is determined in accordance with the respective measured brightnesses. This method is advantageous in that, when the brightness of the main object is different from the brightness of the background, an accurate brightness can be measured, for example, even in back light.
On the other hand, the averaged overall light reading method is a method of finding an averaged value of the brightnesses of a whole range on the screen. The averaged overall light reading method is advantageous over the spot light reading in that it requires only one sensor for light measurement.
However, the above-mentioned averaged overall light reading method has a disadvantage that, if there exists in a part of the screen a bright spot having a great brightness difference, then the exposure is short under the influence of such spot. For example, in the case of back light, while the background brightness is high, the main object is low in brightness since it is in the shade. As a result of this, the difference between the background and main object brightness is large and, therefore, if the averaged overall light reading method is used, then the picture is taken under a condition having an intermediate brightness between the background and main object brightnesses, with the result that the main object is short of exposure while the exposure of the background is excessive.
In view of this, in the case of back light, to solve the short exposure of the main object, a strobe is used to give forth light, that is, a so called day light flash synchronization is used. However, in the averaged overall light reading method with the day light flash synchronization, the background is exposed too much because the brightnesses between the main object and background are not distinguished from each other due to use of only one sensor, while the entire screen is exposed too much because the main object is radiated not only by the strobe light as an auxiliary light but also by the natural light. For this reason, in general, a photographer himself or herself must decide the photographic conditions and correct the exposure.